Red Lines or Artifacts

The red lines that you may be seeing are called "artifacts".
It most likely means that your finger (or ear lobe if you are using an ear sensor) has lost good contact with the sensor. The sensor can't be too loose or too tight. Position your finger tip so that the fleshy part of your finger is directly over the little window on the sensor and you should see the red lines disappear. Experiment with adjusting your fingertip in the sensor or ear sensor clip until you find the best spot. If you feel that the sensor is properly connected and you still continue to have red lines, see Pacemakers and the Freeze-Framer below.